Method of coating



Jan. 12, 1943. c.J. MALM EI'AL. 2,307,783

ammo]: OF COATING Filed May 24, 1959 MELT/N6 POINTS CELLULOSE AC E TATE BUTYRATES Patented Jan. '12, 1943 UNITED SE ATES PATENT GFFICE Marnop or ooa'rnvo Carl J. Hahn and Gerard J. illarke, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application May 24, 1939, Serial No. 275,485

9 Claims. (Cl. 117-65) This invention relates to the coating of objects with cellulose esters in which the coatings are melted on by subjecting the object, containing a layer ofthe ester, to a temperature which will melt but not deteriorate the ester.

The prior art recognizes that cellulose acetate melts at a high temperature whereby it is transformed into a dark-colored, smeary mass. In spite of this characteristic of cellulose acetate, attempts have been made to coat objects in which the ester is heat treated. These attempts have usually involved mixing a large amount of plasticizer with the cellulose ester so that the elevated temperature which is employed forms a solution of the cellulose ester in the plasticizer without being high enough to cause breakdown. The use of a considerable amount of plasticizer in such a composition is detrimental to adhesion,

hence this method has found noappreciable application. It has also been suggested to mix a resin with cellulose acetate which, by treating with heat, melts and dissolves the cellulose ester. Where a. resin has been employed, there is a tendency to brittleness and to discoloration in use and the melting operation may so affect the resin that the transparency of the coating is affected.

An object of our invention is to provide a coating method in which the cellulose ester is melted onto the surface which is to be coated. Another object of our invention is to provide a coating method giving a transparent coating which is free of holes or pores but which is firmly adherent to the surface to which it is applied. A further object of our method is to obtain a protective coating which is non-tacky, stable and of good appearance and which will adhere to surfaces even though there is a greasy or oily film thereon.

We have found that by our coating method, which is based upon the melting point of the cellulose ester, a firmly adhering, strong, non-tacky coating is obtained. We have found that if a layer of a stable cellulose ester, having a substantial content of fatty acid radicals of at least three carbon atoms and a difierence between the melting point and charring point of the ester of at least A 0. and preferably 70 (3., is formed on a surface, such as by spraying or spreading a solvent solution of the ester thereon, and evapcrating the solvent, andthe layer is then heated to the melting point of the ester or sufiiciently nd to cause the layer to become soft and sry without cletrimentally afiecting it and subseouently cooled, a strong bond is obtained between the object and the ester layer and a smooth, brilliant, non-tacky coating is obtained,

this defect a large amount of a solvent was mixed with the cellulose ester and a calendering ratherthan a melting operation was used. We have found that the presence of large quantities of plasticizer or high boiling material mixed with a cellulose ester interferes with the adhesion i such a process. v v

In'our coating methods it is preferred that the composition be substantially free of resins which either cause discoloration of the coating and interfere with transparency or result in a brittle coating or both. It, is also preferred that the composition be free of plasticizer, although the use of some plasticizer does notaffect the adhesion sumciently to prevent its use to a small extent in most commercial applications. Our coating method is preferably carried out by first either dipping an object in a solution of the cellulose ester or by spraying or spreading a solvent solution of the ester on the surface of the object to be protected. Any of the volatile solvents, which will leave a thin layer on an object, will be used. For example, solvents, such as acetone, methyl ethyl ketone, methylene chloride, ethylene chloride or their mixture, either with or without a lower aliphatic alcohol, such as methyl or ethyl alcohol, benzene-alcohol and the like, providing they are solvents of the cellulose ester, are suitable for use. The dilution is optional, but ratios of 4:1 up to 10:1 of solvent to solid are ordinarily quite suitable. After the surface has been wet with the solution, the solvent is evaporated either by subjecting the surface to warm air or by allowing it to stand at room temperature for a sumcient time. The driving of! of the solvent, prior tothe application of. heat for the melting operation, is preferred, although, if desired, driving oil the solvent and causing the melting may be performed in one operation, such as by gradually increasing the degree of heat applied to the coated object. 1

After the solvent has evaporated but before the melting operation, a coating is present on the object which will readily peel off therefrom. To prevent this peeling and to assure a strongly alhering, firm, hard, protective coating, the object is subjected to a temperature above the melting point of the ester but at least 40 0. below its char point until the coating becomes soft and pasty. This melting operation usually takes but ticular ester which is employed.

one or two minutes at a temperature of 20-30' C. above the melting point of the ester. With a temperature not much above the melting point of the ester, a little longer time is necessary, but with layers of the usual thickness, a time longer than four minutes is seldom, if ever, required.

We have found that a temperature'of 230 C. is ordinarily quite suitable for the melting treatment. The temperature employed in our process will usually be found within the range of ZOO-250 C. depending, of course, upon the par- The time is only limited as to length to that which will not detrimentally affect the cellulose ester which is used. After the coating has become soft or pasty, the

object ilowed to cool and has a uniform, firm,

transparent coating thereon. In the coating of objects, the use of a thin layer is preferred because of the rapidity with which it may be softened. For instance, a layer of approximately .001" thickness would ordinarily be very satisfactory. Because of the nature of our process,

it is preferred that the layer be not more than .005" thick, although our invention is not limited as to the thickness of the protective coating applied.

The celluloseesters, which we have found to be most suitable for our invention, are cellulose acetate butyrates containing over butyryl, cellulose acetate propionate butyrates containing over of propionyl and butyryl, cellulose propionate butyrates; cellulose propionates and cellulose butyrates. The butyryl (and/or propionyl) can be replaced by higher acyl radicals, such as valeryl, caproyl or stearyl, but too great a content of acyl groups of more than 6 carbon atoms results in an undesirable softness and .stretchiness in the coatings obtained. It is,

therefore, desirable that the major portion of acyl of at least 3 carbon atoms. should contain between 3 and 6 carbon atoms. If this acyl is our P700858.

of the type containing close to 10 carbon atoms. 1

it is preferred that it be present only in small amount, such as not more than 10-20% of the total acyl of at least 3 carbon atoms.

The esters used in our process should preferably contain at least 20% of a fatty acid radical of above 3 carbon atoms and should contain suf-. flcient higher acyl to asure a melting point of below 230 C. and be of sufllcient stability to have a char point at least 40 C. above the melting point and preferably above 260 C. We prefer to use the fully esterifled ester or one which has been only slightly hydrolyzed as the moisture resistance is higher, the melting point is usually lower and the resistance to actinic rays such as ultra-violet light is much better than in the case of the esters which have been hydrolyzed down as far asthe diester. The accompanying drawing consists of a chart indicating the influence of the acetyl and butyryl content of a cellulose acetate butyrate on the melting point of the ester. This chart shows what acetate butyrates and what straight butyrates, if stable, have a melting point below 230 C. and are therefore teriering with the adhesion of the layer to the object, roughly in proportion to the percentage of plasticizer which is present. If plasticizer is employed, 20% is theupper limit, as the effect upon the adhesion of the coating is particularly noticeable above this point. An amount of plasticizer of 50% or more is undesirable as the adheslon is poor with an amount of plasticizer of this order. If plasticizer or, for that matter, any other compound is incorporated, it should be one which is stable at the temperature employed.

Needless to say, the cellulose ester which is used should also be a stable product. A stable cellulose ester may be defined as one which will withstand heating for eight hours at, 160 0. Any ester, which comes within this qualification which has a melting point below 230 C. and a char point at least 40 C. above its melting point (this indicating stability) may be employed-in If the use of a plasticizer is felt to be necessary, one or more of the following may be incorporated in a proportion which will not seri-. ously sheet the adhesion (below 50% and preferably not more than 20%): dibutyl sebacate,

methyl stearate, triphenyl phosphate and diamyl nhthalate. v I

The presence of resins in. compositions, to be employed in our process, is undesirable, as these compounds in any appreciable amount cause britleness and deteriorate in ultra-violet light. Al-

though the presence of a few per cent (such as up to 3%, the compositions with no more than this being regarded as substantially free of resin); may be tolerated without any serious dlsadvantage. it is preferred that the composition be completely free of resin. If desired, a small amount of wax, such as up to about 5%, can be incorporated in the composition which we employ. For instance, incorporation of a small amount of paraffln wax will result in increased moisture resistance of the coating. If desired,

up to 2% of an anti-oxidant can'be incorporated, which might be of advantage in cases where the esters are subjected to an elevated temperature for a long period so that the charring tendencies are lessened.

The coating of an object in accordance with our invention may be carried out as follows:

One part of cellulose acetate butyrate, having a butyryl content of 3'7 .5% and an acetyl content of 13%, a melting point of 200 C. and a char point of 295 C., was dissolved in 10 parts of ethylene chloride. A brass cup was dipped in the solution and, upon its withdrawal, the solvent was evaporated from the coating. The cup was then put in an oven, having a temperature of 230 C., for two minutes, the coating becoming soft and pasty. It was removed from the oven and cooled and was found to have a firm, tenacious coating; whereas, before the heat treatment, the coating thereon readily peeled off. Pieces of sheet metal, coated in accordance with our invention, were found to crease and bend readily without any break in the protective coatl material, which is not afiected by the tin-e, which is employed in our process.

stance, metal, wood and s1 surf ily coated by our process. Due to the ass rivatives-oi phenols, such as triphenyl phosphate tez-ial should be e p char-ring will not occur under the conditi-n employee. Uperatlcn ate melting ble as indicated by their high :1-

' larly adapted for use in our meth accave ing adhering thereto, which coatingrvas in accordance with our invention. Our coating method may be applied to surfaces which have heen prepared; for coating, such as those which still contain all or grease, in-mail amount. As

of the resulting coating. Our ting method.

may be, applied to the surface objects of and strength or the coating obtained and the resistance oi the coating to ultra-violet light, it is long-lived end serviceable in everyday use.

If the use of a plasticizer is desired some i oi plasticizers which can be used are:

1. Esters of organic dibasic acids and monoar-l alcohols, particularly of the alcohols of at least 4 carbon atoms. such as diamyl plate, ate, dibutyl phthalate and bibutyl sebacate.

2. rs of aliphatic, long-chain .iatty acids end no-hydric alcohols such so methyl or Y M I of aliphatic long-chain alcohols and acids such as cetyl acetate or cetyl propionate.

Instead of the'cellulose acetatebutyrete, prescribed in the example, a cellulose acetate caproate, having the characteristics specified, might be used. Such an ester is a cellulose acetate cap 'roate having an acetyl content of sppromm'ately end a caproyl content '02 approximately 27%, a melting point of ce" C. and e char point of 265 C. This acetate caprte, when melted on the surface of a. sheet of metal, for. i,

examplegives a hard, transparent, ly 1m.

In some the hard ent coating the.

nose of the coating may not be particularly im- 3 portant. In those cases any ester, having a melting point of less than 230 C. and a. char point more than Qabove its melting point, in i1 'lhe preienr'ed coating methmlmvolvec eat the coat srent but rather t e or even energize.

The melting persture should besuch t et'leest 88 C. below the point is ev desirable as with a greater span w;

- mint and the temperature of operation, l 151i e coatings epnlieii m my invention are ew valuable, for eltrical insulating p II==-"'-E due to the uniformityoi the coating. If there are holes in the coating the on or tion removes thme indentations scrim which is unlio u r sage oi electricity. The cellulose esters which pref use in our are th which point. esters stabilized by method claimed in and i p v No. 254,492, filed Feb 8, 1989, are

care

1:. n ce, 7 in accordance with the. procedure 1 ed in the coating to the surface of an object which is not in ur invention in the proportion ified.

e'cl: p i. A method of applying a strongly-adhering acted by moderate heat which comprises wetdose acetate butyrate oi apprte1y:5 21%,

the surface with a solution in a volatile sclvmt oi astalole antially fully esterified celluf ester and at least C. below its char point for approximately two ute end then cooling the material so that a strongly-adhering, nont coating is formed thereon. 1

2. A method of op ected by moderate heat which the surface ith a solution in a volatile sob rent of a stable substantia 1y ly cello:-

butyrate oi approately 541% acetyl, the inder oi the ecyl or ,5 i and not more than 5% of was.

p'omtlne ofl the solvent and subiecthe tely V c-minutes andcoo the so that a steely-adhering... -"v

" coating is formed thereon.

re ventci coot to the surieceof an objec w vent of a celluloseester'aelected from the a. a method or appl ected by moderate heat, which comprlses wetting the surface with a solution in a volatile col- M of the cellulose acetate butyratee dfelimo'se i T 0% of p11 an evarating o the r to n which mint without detrime'ntally cot which t comp weti. inavola e'aola; it the group molecular weight and are suitable for u e 1 p a strly- .z; e coating. to the surface of an object which is not antially butyryl, containing substantially no plea.

56 C. w its char int 7 l e e object as the we nit which la at le cc of the and cooling the object so that consisting of the cellulose acetate butyrates and the cellulose acetate caproates having melting points of less than 230 C. and char points at least 40 C. above their respective melting points, which ester contains 20% of plasticizer and'is substantially free of resin, evaporating oil thesolvent and subjecting the object having the cellulose ester layer thereon to a melting temperature for the ester which is at least 40 C. below its char point and will not detrimentally affect the ester and then allowingthe object to'cool so that a strongly-adhering, firm,'nontacky coating is formed thereon.

5. A method of applying a strongly-adhering coating to the surface 0! an object which is not aiiected by moderate heat, which comprises wetting the surfacewith a solution in a volatile solvent of a cellulose acetate butyrate having a melting point 01' less than 230 C. and a char point at least 40 C. above its melting point, which ester contains 020% of plasticizer and is substantially free of resin, evaporating oh the solvent and subjecting the object having a layer of the cellulose ester thereon to a temperature which A will melt the ester without detrimentally aflecting it and then allowing the object to cool so that a strongly-adhering, firm, non-tacky coating is formed thereon.

6. A method of applying a strongly-adhering coating to the surface of an object which is not affected by moderate heat, which comprises wetting the surface with a solution in a volatile solvent ot a stable, substantially-fully esterliied eel lulose acetate butyrate of approximately 5-21% acetyl, the remainder of the acyl being substan- 8. A method or applying a strongly-adheringcoating to the surface of a metal object which is not aflected by moderate heat, which comprises wetting the surface to be coated with a solution in a volatile solvent of a cellulose ester selected from v the group consisting oi. the cellulose acetate butyrates and the cellulose acetate caproates having melting points of less than 230 C. and char points at least C. above their respective melting points, which ester contains 040% of plasticizer and is substantially free 01' resin, evaporating of! the solvent and subjecting the object having a layer oi. thecellulose ester thereon to a temperature which will melt the ester without detrimentally aflecting .it and then allowing the' coating to cool so that a strongly-adhering, firm,

non-tacky coating results.

- 9. A method of applying a strongly-adhering coating to the surface 01 an object which is not affected by moderateheat, which comprises wet ting the surface with a solution'in a volatile soltially butyryl, which ester contains 0-20% of plasticizer and is substantially free of resin, evaporating oil the solvent and subject the object to a temperature which will melt the ester without detrimentally affecting it and then allowing the object to cool so that a strongly-adhering, firm, non-tacky coating is formed thereon.

7. A method of applying a strongly-adhering coating to a smooth surface which is not aflected by moderate heat, which comprises wetting the surface with a solution in a volatile solvent of a cellulose ester selected from the group consisting or the cellulose acetate butyrates and the vent or a cellulose .ester selected item the group consisting oi'the cellulose acetate butyrates and points orless than 230 C. and char points at least 40 0. above their respective melting points, containing substantially no plasticizer or resin, evaporating oil the solvent and subjecting the object having the layer of cellulose ester thereon to a temperature which will melt the ester without detrimentally affecting it and then allowing the material to cool so that a stronglyadhering, firm, non-tacky coating is formed thereon.

'GERARDLCLARKEQ the cellulose acetate caproates having melting. f 

